1. Field of the Invention
This invention relates generally to conjugated linoleic acid (CLA)-rich oil production from linoleic rich vegetable oils by heterogeneous catalysis, and more particularly to a process for producing conjugated polyunsaturated fatty acids (PUFA) in triglyceride form, preferably CLA-rich oils, by isomerization of a non-conjugated PUFA in vegetable oils using a heterogeneous transition metal catalyst promoted by an organic acid or thiol-containing compound.
2. Description of the Related Art
CLA is found naturally in dairy and beef products generally at levels of approximately 0.3-0.8% (w/w) of the fat as bovine rumen fermentation products. The current human intake of CLA is, however, approximately ten (10) times less than the 3 g/day minimum value recommended as being necessary to produce desirable physiological health effects. Obtaining the estimated optimum dietary CLA levels from natural beef and dairy sources would increase the total fat and saturated fat intake and increase the negative health risks associated with dietary animal fats.
CLA is a group of positional and geometrical isomers of linoleic acid with conjugated double bonds. The most common CLA isomers are cis-9, trans-11-octadecadienoic acid and trans-10, cis-12-octadecadienoic acid. CLA has anti-carcinogenic, anti-atherogenic, anti-diabetic and anti-obesity properties, along with the ability to increase lean body mass, to protect against immune induced body wasting disease, chronic inflammatory disease, cancer and to provide other positive health effects. CLA decreases fat and increases muscle content in the human body, reduces inflammation, shows a beneficial effect on bone formation, enhances immune functions and reduces asthma. A recent study suggests that CLA-rich soybean oil with a high percent of trans, trans CLA also exhibits beneficial health effects. Therefore, a concentrated source of dietary CLA that is low in saturated fat and cholesterol is desirable.
Soy oil is the most commonly used vegetable oil in United States, and it contains about 55% linoleic acid. Other vegetable oils high in linoleic acid include sunflower (57%), corn (55%), cottonseed (50%) and peanut (50%). Due to their technological and nutritional applications, several isomerization reactions have been developed to convert fatty acids in vegetable oils with isolated double bonds into fatty acids with conjugated double bonds. Historically, CLA fatty acid has been produced by fermentation and enzyme technology. A recent approach to CLA production includes isomerization of linoleic acid rich oil to CLA under alkaline conditions, with the aid of alkali bases or sodium methoxide dissolved in DMSO or propylene glycol, and subsequently neutralizing the alkali bases with acid. The alkaline catalytic process, however, is unable to directly produce CLA-enriched vegetable oils because of competitive hydrolysis of triacylglycerol (TAG).
CLA in vegetable oil has also been produced by converting linoleic acid to CLA using homogeneous isomerization with transition-metal catalysts, such as using iodine by homogeneous photo-catalysis. A drawback of these processes is the removal of the soluble catalyst from the CLA-rich oil before the product is suitable for human consumption.
Heterogeneous catalysis isomerization is another process utilized in CLA production, and more readily allows for catalyst separation from the CLA-rich oil. These isomerization techniques, however, have generally involved linoleic acid fatty acids or methyl linoleate isomerization in solvent-based systems.
Although a variety of methods aforementioned have been reported for producing CLA from free fatty acid and TAG forms and occasionally refined, bleached and deodorized oil, there remains a need for an improved process for producing high yields of CLA-rich vegetable oil from linoleic rich oils using heterogeneous catalysis with minimal catalyst residue.
It is further desirable to provide a process for producing conjugated PUFA in triglyceride form, preferably CLA-rich oils, by isomerization of a non-conjugated PUFA in vegetable oils using a heterogeneous transition metal catalyst promoted by an organic acid or thiol-containing compound.
It is still further desirable to provide a process of producing an enriched vegetable oil having in excess of 20% CLA using heterogeneous catalysis isomerization in the presence of a transition metal catalyst and a promoter using steam/vacuum distillation, hydrogenation and/or deodorization.
It is still yet further desirable to provide a process for producing a CLA-rich oil that requires only minimal post-processing catalyst removal.
It is still yet further desirable to provide a process for producing CLA-rich oils using heterogeneous catalysis that is an environmentally-friendly process in contrast to alkali isomerization.
It is still yet further desirable to provide a process for producing CLA-rich oils using heterogeneous catalysis that does not require any solvent or any chemical other than a catalyst and a promoter.
It is still yet further desirable to provide a process for producing CLA-rich oils from using heterogeneous catalysis in the absence of iodine and with a metal catalyst that can be easily removed and reused.
It is still yet further desirable to produce CLA-rich oils using a single step transition metal-based heterogeneous catalysis process that uses a significantly reduced amount of catalyst dose with refined, unbleached soy oil (RUBSO).
It is still yet further desirable to provide a process for producing CLA-rich oils with little to no trans-fat using transition metal-based heterogeneous catalysis with organic acids and thiol promoters to enhance the catalytic conversion rate of linoleic acid to CLA in vegetable oils.
Other advantages and features of the invention will be apparent from the following description and from the claims.